RMI EJB 2 / EJB 3 interoperability between JBoss EAP 4 / 5 and JBoss EAP 6

Issue

• We have a lot of applications and services running on JBoss 4.3. They currently operate mainly through RMI calls (using Stateless EJB 2.1).
  Our main concern in introducing JBoss EAP 6 is to make JBoss 4.3 and 6.0 operating on the RMI protocol. This would allow us to migrate applications and services on a long period.
• Which is the best way to make JBoss EAP 6 to invoke a Stateless EJB 2.1 on JBoss EAP 4.3 (CP09)? Which features would we lose (security, transactions propagation)?
• Then, is it possible to have JBoss EAP 4.3 calling JBoss EAP 6.0 via RMI (EJB 2.1 or EJB 3)?
• I have an application in JBoss EAP 6 and it needs to communicate with an application on JBoss 5 via RMI.
• Do you have a guide to make JBoss EAP 6 make RMI calls to JBoss 5?
• Remove EJB invocation between EAP 4.2 and EAP 6
• Do you have any information how to call EJBs in EAP 5 from an application running on EAP 6?
• How to implement jnp protocol that can be used withing jboss eap 6? How to check the status of jboss eap 4.3, we use jnp and there are jnp client classes under server/lib directory so till now it worked fine, however now while migrating to jboss 6, existing jboss 4.3 can't be controlled as jboss 6 does not have any jnp implementation. So is it possible to create a module from JBoss EAP 4.3 jnp implementation for jboss eap 6.x? If yes then which libraries do we need to include in that module?